[50.20] Astrometric Stability of the Radio Continuum Nucleus in the Seyfert~1 Galaxy NGC\,5548

J.M. Wrobel (NRAO), J.E. Conway (OSO), R. Terlevich (RGO)

The NRAO VLA and VLBA were used at 8.4~GHz to monitor the
astrometric stability of the radio counterpart to the broad
line region (BLR) in the Seyfert galaxy NGC\,5548. The
position of the radio continuum nucleus was stable to an
accuracy of: [1] 20~mas (6.4~pc) between VLA and VLBA
observations separated by 2.4~years, [2] 20~mas (6.4~pc)
between VLA and VLBA observations separated by 5.5~years,
and [3] 1.8~mas (0.58~pc) between two VLBA observations
separated by 3.1~years. This stability is consistent with a
black hole being the ultimate energy source for the BLR.
Such stability is improbable with star cluster models which
treat the BLR as a compact supernova remnant and, for
NGC\,5548, require a new supernova event every 1.7~years
within a region of diameter 48~pc (150~mas). The NRAO is a
facility of the National Science Foundation operated under
cooperative agreement by Associated Universities, Inc.

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